up button for width of stroke should be disabled for a group

[v1nce]

ubuntu 12.04 FR-fr inkscape 12832

draw paths
group them
fill & stroke => the width of stroke = 0 (this makes sense because one can group paths with different width)
BUT the up button next to width text box is still enabled =
if you press it, the width text box displays garbage (from between 0,000 and 0,900 then reset to 0,000)
while the width pf paths grow or shrink asynchronously (depending on refresh rate)

[su_v (suv-lp)]

AFAIU this is already reported and tracked in
- Bug #734596 “Increasing stroke width on grouped objects evokes erratic behavior”
  <https://bugs.launchpad.net/inkscape/+bug/734596>